American drivers spend an average of 41 hours a year in traffic at peak commuting hours, one analysis found

PHILADELPHIA—Traffic crawls along downtown’s Chestnut Street, horns honking as cars block the intersection. Up ahead, construction claims one of three lanes, and a Canada Dry delivery truck is parked in the bus lane, forcing city buses to squeeze by.

Similar scenes play out every day in cities across America. In six of the 10 most populous cities, including Philadelphia, average midday vehicle speeds in the downtown core have slowed between 3.8% and 10% since 2015, according to an analysis for The Wall Street Journal by transportation...